1. Field
Embodiments disclosed herein generally relate to data storage systems, and more particularly, to heat-assisted magnetic recording (HAMR) heads.
2. Description of the Related Art
Higher storage bit densities in magnetic media used in disk drives have reduced the size (volume) of magnetic bits to the point where the magnetic bit dimensions are limited by the grain size of the magnetic material. Although grain size can be reduced further, the data stored within the magnetic bits may not be thermally stable. That is, random thermal fluctuations at ambient temperatures may be sufficient to erase data. This state is described as the superparamagnetic limit, which determines the maximum theoretical storage density for a given magnetic media. This limit may be raised by increasing the coercivity of the magnetic media or by lowering the temperature. Lowering the temperature may not always be practical when designing hard disk drives for commercial and consumer use. Raising the coercivity, on the other hand, requires write heads that incorporate higher magnetic moment materials, or techniques such as perpendicular recording (or both).
One additional solution has been proposed, which uses heat to lower the effective coercivity of a localized region on the magnetic media surface and writes data within this heated region. The data state becomes “fixed” once the media cools to ambient temperatures. This technique is broadly referred to as “thermally assisted (magnetic) recording” (TAR or TAMR), “energy assisted magnetic recording” (EAMR), or “heat-assisted magnetic recording” (HAMR) which are used interchangeably herein. It can be applied to longitudinal and perpendicular recording systems as well as “bit patterned media”. Heating of the media surface has been accomplished by a number of techniques such as focused laser beams or near-field optical sources.
Typically, the HAMR head includes two optical components: a microphotonic spot-size converter (SSC) and a near field transducer (NFT). SSC converts a highly-divergent output of an external semiconductor laser diode into a well-confined mode that couples into the NFT. The NFT is a plasmonic nano-antenna that further focuses the light into an ultra-small spot-size for high-density magnetic recording. However, the profile of the laser diode is typically asymmetric in the fast axis, while the mode profile of the SSC is typically symmetric. This intrinsic mismatch in symmetry results in unwanted coupling loss. In addition, the misalignment tolerance between the laser diode and the SSC is small, which increases the assembly cost and reduces manufacturing yield. Therefore, there is a need in the art for an improved HAMR heads.